Study: What happens in the blood of a runner during extreme exertion?

After extreme exertion - for example, one hour run until exhaustion - the level of circulating free DNA in the blood dramatically increases. This marker is associated with tumours, inflammations or cell necrosis. Research of scientists from Łódź sheds new light on this issue.

"It is well known that intense physical activity causes stressful metabolic reactions in the body. People have died during severe physical exertion" - reminded Prof. Dariusz Nowak of the Medical University of Lodz. "But only recently it has been discovered that after heavy exercise the amount of circulating free DNA (cfDNA) in the blood increases considerably".

The researcher explained that DNA in the human body usually occurs inside cells - in the nucleus (nuclear DNA) or in mitochondria (mtDNA). However, free fragments of DNA can appear in the blood plasma. Increasing the concentration of such extracellular DNA usually does not indicate positive phenomena in the body. It is a factor associated with the destruction of cells: by cancer, inflammation, autoimmune diseases or complications during pregnancy.

Now it turns out that these are not the only reasons. Research conducted at the Medical University of Lodz shows that after one hour run until exhaustion, the level of cfDNA is 10 times higher than before the run. Similarly, but not so clearly, the level of free extracellular mtDNA grows. "We will investigate the consequences of this" - noted Prof. Nowak.

A group of 11 healthy men participated in the experiment at the Medical University of Lodz. The subjects\' oxygen limit (maximal oxygen uptake) was tested. And then training on the treadmill began under controlled conditions. Each participant would run at a pace that suited their ability, at a treadmill speed corresponding to 70 percent of each person\'s maximum oxygen uptake. "It was a run until exhaustion" - said Nowak. He added that the participants would run as long as they could- until they could no longer maintain the speed that the treadmill imposed on them. "It took an average of one hour. Some would run, for example, 8 km, others 12 km" - said the scientist. Each of the subjects completed three such training sessions - separated by three days of rest.

Both before and after training, the level of circulating free DNA in the runners\' blood was checked. The researchers wanted to check whether the organism would get used to extreme exertion and the level of cfDNA after subsequent workouts would be lower. "We assumed that tolerance would develop after a few rounds of exertion" - said Prof. Dariusz Nowak. However, the tests showed that this was not the case - even after several regular workouts the level of cfDNA still increased like after the firs workout. There were no exceptions among the subjects.

"In this case, the presence of cfDNA in the blood probably does not indicate the destruction of cells in the mechanism of necrosis or apoptosis" - the researcher told PAP. After the death of each cell, the DNA in it must be disposed of by the body, he explained. But from damage to the cell five hours usually pass before the DNA reaches the blood. "In this experiment, DNA fragments appeared in the blood just after the run, which lasted about an hour. That was too fast" - the scientist noted.

He said that a possible explanation was that cfDNA in the blood of a runner could come from white blood cells or platelets. "They would use molecules of DNA to create something like a net for catching and killing bacteria" - compared Prof. Nowak. In this case, DNA would play a different role than that of a genetic information carrier. The expert reserved that this was only a hypothesis.

In future research, scientists want to check whether the effect of elevated cfDNA can also be observed in women. This will be more difficult, because the body\'s capability of extreme effort varies within the sex cycle.

"I also want to check the length of the so-called telomeres in people whose profession involves running or exertion" - said the researcher from the Medical University of Lodz. The shortening of telomeres - DNA fragments at the ends of chromosomes - could be point to accelerated aging processes.

"We should consider whether long-distance running really is a way of maintaining youth" - commented Prof. Nowak. He emphasised that physical exercise is beneficial for health, but only if it is moderate. "When the exertion is too large, it becomes harmful. The body can only take so much punishment" - he concluded.